This invention is related to sound actuated switches and in particular a switch which is actuated by a sound of sufficient magnitude to turn the switch on for a predetermined period of time and to maintain the switch on for as long as sounds of sufficient magnitude are received.
One use of sound actuated switches is as a burglar deterrent. Certain burglar deterrent devices actuated by sounds, as exemplified by U.S. Pat. No. 4,099,168, are sensitive to certain types of sounds, such as that of breaking glass or splintering wood, which signal a forced entry. U.S. Pat. No. 4,103,294 discloses a different type of sound actuated burglar deterrent. The device acts as a switch which illuminates a light for a period of time, say five seconds, in response to a sound and extinguishes the light for another period of time, say three seconds. Continuous noise causes the continuously alternating illumination and extinguishment of the lights to scare the burglar away.
It may be desired to use a sound actuated switch in a commercial establishment in lieu of or in addition to a standard light switch so that when there is little activity in the room, the lights would automatically shut off. When so used they would be both a convenience and an energy saver. Such switches could also be used in situations when it would be impractical or difficult to reach a light switch, such as in a dark hallway or in a garage or when the switch is behind a piece of furniture.
Unfortunately, because of their specialized operational characteristics, such burglar deterrent sound actuated switches are not particularly suited for many other uses. First, the circuitry is often sensitive to only higher frequency noise. Normal speech is often ineffective. Second, burglar alarm type switches commonly require that the sound be maintained for a certain period, generally to avoid "false alarms." Third, the circuitry of the prior art burglar alarm type of sound actuated switch does not particularly lend itself to individualized, flexible operation, such as the timing of the period during which the switch is left on in response to a noise. Of course switches which flash the lights on and off are unacceptable for normal use.
Another drawback with the prior art sound actuated switches is that their internal power supplies are usually somewhat inefficient. Commonly, the power supply for the switch incorporates one or more zener diodes, a rather inefficient method of producing direct current. Such a power supply would generally not be particularly suitable for enclosing within a box with a wall (such as a replacement for a standard wall switch) because of the heat generated.
Thus, while the concept of a sound actuated switch is attractive, the lack of flexibility and energy efficiency has prevented the potential benefits from being realized on any substantial scale.